1. Field of the Invention
The present invention deals with a foamed polyurethane composition that is both flame retardant and low smoke generating. In one embodiment, the flame-retardant, low-smoke generating polyurethane foam is comprised of the condensation product of a polyisocyanate with a halogen-containing polyol and, having added thereto, the metallic salt of a polyfunctional aromatic carboxylic acid free of acid functionality.
2. Description of the Prior Art
Increasing attention has been placed on the flammability and the quantity of smoke generated from polyurethane foams. Methods to measure and rate such smoke generation have been promulgated, for example, as seen in ASTM-E84 Tunnel Test as well as in UL-723. Also see Journal Cellular Plastics, January 1967, pages 41 to 43. Flammability rates of such polyurethane foams have also been measured and one of the most acceptable standardized tests for such polymeric systems is ASTM-E84 (UL-723).
The use of certain additives for the purpose of reducing the flammability of polyurethane materials and polyurethane foams is well known to those skilled in the art. Among the wide variety of additives currently employed for such use are the various types of phosphorus-containing compounds. These phosphorus compounds are generally used either alone or in combination with other materials, such as organic or inorganic compounds of antimony or halogenated organic materials. The phosphorus-containing compounds may be non-reactive chemicals such as tris(2-chloroethyl)phosphate, tris(2,3-dibromopropyl)phosphate, ammonium phosphate or more complicated hydroxy compounds which are reacted into the foam structure. Similarly, a wide variety of halogen-containing polyols are also known to reduce flammability and flame retardancy when such are incorporated into the polyurethane polymer and, as in the case of the phosphorus compounds, such may also be of reactive or non-reactive type. Antimony trioxide is also used to reduce the flammability of urethanes, especially in combination with other materials such as the aforementioned halogenated organics and ammonium phosphate.
Flame retardant and thermally stable polyurethane materials have been disclosed that are formed from a mixture of a polyfunctional aromatic carboxylic acid, a polyol and a polyarylpolyisocyanate, for example, see U.S. Pat. No. 3,637,543. These modified polyurethanes have been described as generating much less smoke than prior art foams. In U.S. Pat. No. 3,684,748, it is disclosed that carboxylic acid anhydrides in combination with phosphorus-containing polyols form a synergistic combination of components that give effective flame retardancy. Aliphatic carboxylic acids are noted to inhibit flame spread in combination with polyether polyols and phosphorus-containing polyols, see for example U.S. Pat. No. 3,639,307.
One of the drawbacks of these known compounds and combinations of compounds, however, has been the fact that generally large amounts (up to 35%) of the additive must be incorporated into the urethane polymer in order to render it acceptably flame resistant and low smoke generating. Such large quantities of additives often have a deleterious effect upon the properties of the foam. Foams can be weakened and may show a tendency to shrink. Some additives tend to crystallize or migrate out of the foamed polymer after a relatively short time of incorporation therein. In many cases, the molecular integrity of the flame-resistant polymer is drammatically changed through the incorporation of flame-retardant compounds. This results in an overall degradation of both physical and chemical properties. In addition, the low-smoke generating carboxylic acid containing polyurethane foam compositions do not effectively cure in commercially attractive time periods because polymerization is substantially inhibited by the presence of these compounds. In many cases, no foam is produced or, at best, an extremely high density foam results.